Hi @ISC_SG_SciPub, all Crossref metadata is open by default, and we’re committed to the open governance, sustainability, and insurance principles set out by POSI, which also calls for broad stakeholder oversight (drawn from 17.5k members which include universities, academies of science, funding orgs, libraries, and publishers both non-profit and for-profit. See our latest report on how we’re meeting those principles. So all the metadata is open without restriction, forever, and therefore linkable with any other system that can read and ingest JSON, which includes the many thousands of discovery and analytics services out there and tools built on this metadata. As you note, we’re planning to extend the schema to accept other identifiers in relationships too, like other parts of the schema.
Let us know if you want to chat more about the work of the Preprint Advisory Group or anything else metadata-y.